The modern theory of evolution includes both Darwin

1
Modern Evolution
The modern theory of evolution includes both
Darwins ideas of variation and natural selection
and the current knowledge of the sources of
variations.

1. Segregation and the recombination of alleles
   during sexual reproduction.
2. Gene mutation occurs spontaneously or may be
   caused by mutagenic (mutation causing) chemicals.

2
Natural Selection

• Natural selection involves the struggle of
  organisms to survive and reproduce in a given
  environment
• Traits which are beneficial to the survival of an
  organism tend to be retained and passed on, and
  therefore, increase in frequency within a
  population
• Traits which have low survival value to an
  organism tend to diminish in frequency from
  generation to generation. These are selected
  against.
• If environmental conditions change, traits that
  have low survival value may now have a greater
  survival value. Therefore, traits that prove to
  be favorable under new environmental conditions
  will increase in frequency

3
Geographic Isolation

1. Isolation of a population increases the chances
   for speciation (the development of a new species)
   by separating a small group of organisms from the
   main population with its large gene pool
   (inheritable traits)
2. Changes in gene frequency are more likely to
   occur in small populations than in large ones
3. Geographic isolation of a population is caused by
   natural barriers like mountains, large bodies of
   water, and deserts

4
4. The evolution of an isolated population into a
new species may involve the following factors
a) the gene frequency in the isolated
population may have been different than the gene
frequency in the main population to begin with
(founder effect) b) different mutations occur
in the isolated population and in the main
population c) different environmental factors
may also have exerted different selection
pressures on each population (natural selection
was different)
5
Reproductive Isolation

• If the isolated population becomes so different
  from the main population that members of the two
  cannot interbreed, even if the geographic
  barriers are removed.
• When two populations can no longer interbreed and
  produce fertile offspring, they have become two
  distinct species.

6
Time Frame for Evolution
Gradualism- proposes that evolutionary change is
slow, gradual, and continuous Punctuated
Equilibrium- proposes that species have long
periods of stability (several million years)
interrupted by geologically brief periods of
significant change during which a new species may
evolve. This could be caused by drastic
environmental changes, such as global cooling or
warming. Environmental changes such as these
could also cause an extinction.
7
Heterotroph Hypothesis

• This is one proposed explanation for how life
  arose and evolved on primitive earth.
• According to the Heterotroph Hypothesis, the
  first life forms were heterotrophic and had to
  obtain their nutrients from the environment.

8
Primitive Earth

• Earth was very hot consisting of inorganic
  substances in all states solid, liquid, and gas.
  And the land was still forming from cooling
  lava.
• The atmosphere consisted of water vapor,
  hydrogen, methane gas, and ammonia (No Oxygen)
• As the earth cooled, water vapor condensed in the
  atmosphere and rain fell forming seas described
  as hot, thin soup, full of dissolved minerals
  from the land.
• In addition to the extreme heat, there was
  electrical energy in the atmosphere causing
  lightning, radiation from the Sun (because of the
  lack of an established atmosphere), and
  radioactive gasses being given off from
  radioactive rocks cooling.

9
Synthesis of Organic Compounds

• The inorganic molecules in the seas chemically
  bonded to form organic molecules, including
  simple sugars and amino acids.
• These organic molecules became the building
  blocks for the first life forms.
• Scientist Stanley Miller created an apparatus
  that simulated the conditions on the early Earth.
  His experiments showed that dissolved gasses
  could combine to form simple organic compounds,
  in the presence of heat and electrical energy.

10
(No Transcript)
11

• Some of the large complex molecules formed
  groupings or clusters called aggregates
• These aggregates developed a surrounding
  membrane
• It is believed that aggregates absorbed simple
  organic molecules from the environment for food
• Therefore, they carried on a form of
  heterotrophic nutrition
• Over time, the aggregates became more complex and
  highly organized.
• Eventually they developed the ability to
  reproduce and were therefore considered living
  cells

12

• It is thought that these early heterotrophic life
  forms carried on a form of anaerobic respiration
  known as fermentation
• As a result of the extended periods of
  fermentation, carbon dioxide was added to the
  atmosphere
• Eventually, as a result of evolution, some
  heterotrophic forms developed the capacity to use
  carbon dioxide from the atmosphere to form
  organic compounds (food)
• These organisms were the first autotrophs
• Some bacteria are autotrophs, but most of the
  autotrophs today are green plants and algae.

13
Anaerobes to Aerobes

• Photosynthesis from the autotrophs added oxygen
  molecules to the atmosphere. Eventually the
  atmosphere was filled with O2.
• Over time, both autotrophs and heterotrophs
  evolved the ability to use oxygen for respiration
  (became aerobic, instead of anaerobic), because
  it was more efficient than what they were doing.
• There are both heterotrophic and autotrophic
  (plants) organisms on the Earth today.
• Presently, most life forms use aerobic
  respiration today, although there are still some
  anaerobic organisms around.

14
3 Modern theories of continuous evolution
Divergent Evolution, Convergent Evolution, and
Parallel Evolution. All of them seem to occur at
different times.
15
Divergent evolution  -  Pattern of evolution in
which two closely related species gradually
become more and more dissimilar.
When people hear the word "evolution," they most
commonly think of divergent evolution, the
evolutionary pattern in which two species
gradually become increasingly different. This
type of evolution often occurs when closely
related species diversify to new habitats. On a
large scale, divergent evolution is responsible
for the creation of the current diversity of life
on earth from the first living cells. On a
smaller scale, it is responsible for the
evolution of humans and apes from a common
primate ancestor.
16
Convergent Evolution Convergent evolution
causes difficulties in fields of study such as
comparative anatomy. Convergent evolution takes
place when species of different ancestry begin to
share analogous traits because of a shared
environment or other selection pressure. For
example, whales and fish have some similar
characteristics since both had to evolve methods
of moving through the same medium water.
17
Parallel Evolution Parallel evolution occurs
when two species evolve independently of each
other, maintaining the same level of similarity.
Parallel evolution usually occurs between
unrelated species that do not occupy the same or
similar niches in a given habitat.
18
(No Transcript)